Physical and chemical techniques will be developed for the analysis of the structure of complex macromolecular assemblies or organelles. The major goal is information on the conformation of individual assembled components and proximity relationships between components. Techniques will include singlet energy transfer fluorescence, breakable photocrosslinkers, phototransfer reagents and dye photosensitized chemical modification. A variety of potential uses for immunoglobulins and fragments directed against fluorescent dyes will also be explored including electron microscopy and affinity chromatography. These techniques will be applied to several different systems including the conformation of ribosome bound tRNA's, structure of several ribosomal proteins, free and in the intact ribosome, the topological arrangement of proteins in the ribosome and proteins which form the lytic lesion of the mammalian complement system, complement protein-membrane interactions, and elements of the cell surface involved in cell-cell recognition. A few shorter range projects including conformation of nucleic acids with covalently attached carcinogens and mechanism of microtubule disassembly should be completed early in the project period. BIBLIOGRAPHIC REFERENCES: Langlois, R., Kim, S. H. and Cantor, C. R. (1975). A Comparison of the Fluorescence of the Y Base of Yeast tRNA phe in Solution and in Crystals. Biochemistry, 14, 2554. Gaskin, F., Cantor, C. R. and Shelanski, M. L. (1975). Biochemical Studies on the In Vitro Assembly and Disassembly of Microtubules. Ann. N. Y. Acad. Sci., 253, 133.